Sealing Between Sheets of Aluminum before Riveting

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Whalensdad

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To start, my trailer is totally gutted as I am redoing it. It is aluminum skinned, built in the 40's, and resembles an Airstream (but it is not). The previous owners had had some leaks and instead of repairing they gooped on a bunch of fiberglass along the leaking seams. I've removed the fiberglass and rivets from about an 8 ft section of my roof and will clean out the dirt and grime between the overlapping sheets of aluminum. I found some hard deteriorated rubber between the sheets that was used when the RV was first built. What should I put between the 2 sheets of aluminum to ensure there is a watertight seal before I rivet the sheets back together?:
1. A thin sheet of rubber like what was originally used
2. A thin layer of TremPro 635 Polyurethane
3. A thin layer of Silicone sealant

I plan on purchasing Olympic Shaveable Rivets for rejoining the sheets.

Thanks,
Lee
 
To make the aluminum sheets look proper, and fit proper, you'd want something to make the same spacing as the original rubber. Which would make a rubber strip the easy choice, if it were available. If one were to use some type of caulk sealant you'll have a problem with it squishing out to virtually nothing for spacing and nothing for sealing at the rivet, when you rivet. One could use bolts and nuts to approximate the correct panel fit, clean the excess, allow to dry, then rivet for a thickness correct, good seal. Lots of work, but maybe worth the effort if the rubber is hard to find or if you feel the rubber won't provide the seal you want. I don't know the rivet spacing and the aluminum panel fit. If there are some spots that need a little more sealing than others, maybe a combination of caulk and rubber strip.

I'm sure you already know, but if you'll put a stripe of 2" masking tape right along the seam (on the bottom most panel) prior to putting whatever sealant into the joint then you can pull it off after the joint is fastened, leaving a nice clean line. All the excess caulk is on the tape.

As for type of sealant if you go that way, I'd want something that can be taken apart again whenever a leak occurs or if damage to a panel occurs. So I wouldn't use any permanent type adhesives.

Ken
 
Go to a bicycle shop and look at the rubber strip that goes around the  inside of the rim to protect the tube from the spoke heads. That might work.
 
halfwright said:
Go to a bicycle shop and look at the rubber strip that goes around the  inside of the rim to protect the tube from the spoke heads. That might work.

I was actually thinking about that as a possibility.
 
NY_Dutch has the best idea.  It is a rubber strip with adhesive on both sides.  Have used it to seal seams in marine use and works well. 
 
Whalensdad said:
How about Butyl Tape (TremPRO 691)?

Probably would work well. As long as you have the sheets totally off. How would you slide sticky tape between areas that aren't completely disassembled? Your post doesn't really give us a clear picture whether you've totally removed the panels or you've taken the rivets out and will "clean out the dirt and grime between the overlapping sheets of aluminum". My mental picture of how far apart you've taken the panels shows you trying to slide something between the panels.

Ken
 
Here are some pictures of what I'm dealing with.

Over the past 24 hours I've come up with a few options.

1. Use butyl tape in all of the areas I can get easy access too. That would be mainly on the top and partially down the sides. Areas where I can't get easy access to for butyl tape, I would use the rubber that goes inside a bicycle rim to protect the tube. I would then rivet this down using shaveble head rivets using the current set of holes. Once that is done I would liberally apply sealant along the inside seam and rivet bottoms. -- My concern is being able to align all of the holes since the butyl tape will not allow me to see through.

2. My second option is to use the butyl tape and rubber as before but use standard pop rivets. Once they are attached I would liberally apply sealant on top of the rivets and along the outside seam and then I would attach a band of aluminum from one side of the trailer over the rivets, seams and sealant to the other side. This I would rivet using shaveable head rivets. In effect the original rivets and seam would be covered by this band of aluminum.

 

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From what I see in the pictures, I think I'd go with a caulk type adhesive. It can be pushed down into every place that you haven't taken the rivets loose providing a better seal, IMHO, than the rubber or butyl tape will. I'd use small bolts in every other or every third hole to squeeze out the excess, clean up the squeeze-out and let it cure. Then go back and rivet for looks. Since it appears the final finish is going to be paint, you could even use some filler in areas to fair the metal as needed.

Ken
 
I'm thinking of using Vulkem 116 (I can't find Trempro 626 or 636) instead of caulk. I like the idea of using bolts to sandwich the sheets together until they cure.I'm just hoping that the bolts come out easily.
 
I would use butyl tape where I could and use caulk in the places that are difficult. I wouldn't use a household caulk but an automotive type RTV gasket making caulk that is meant to be compressed rather than a household caulk that is designed to fill and seal a void. Read the directions on the caulk as many want you to allow the caulk to skin for 5-15 minutes before assembly. This helps seal better as the caulk is now flexible instead of oozing out when you rivet and then the metal relaxes leaving a potential leak. If you are going to paint it afterwards then you can follow up with a good caulk on the outside seams and drag your finger to remove the excess. You have to keep in mind the frame and seams flex with movement and temperature so you need a flexible seal.

Another thought is places like Advance Auto Parts, NAPA, etc sell sheets of gasket making material to include rubber and cork. You could cut your own rubber strips. The rubber I bought was about 1/16" thick.
 
You have quite a project. You will need Clekos or enough setup bolts to hold it together you can rivet it before it dries or wait.  If you want it to seal look hear.
http://www.aircraftspruce.com/pages/cs/fueltanksealants/ac236b4.php
Bill
 
WILDEBILL308 said:
You have quite a project. You will need Clekos or enough setup bolts to hold it together you can rivet it before it dries or wait.  If you want it to seal look hear.
http://www.aircraftspruce.com/pages/cs/fueltanksealants/ac236b4.php
Bill

Probably the best answer yet!
I was wondering the other day when reading this thread what they used for the aircraft skins for those bladderless integral tanks, and for the general fuselage seals between skin panels!
perfect!
 
Good ideas, but don't Clekos hold the pieces tightly together? I think Whalensdad needs to have the sealant stay between the sheets until cured and then the rivets will hold the pieces in place. If it's squeezed out before cured, then the seal may be compromised.

I see the fuel tank sealant is also an adhesive. If you glue it together with a permanent sealant/adhesive then any future repairs would be extremely complicated or impossible. For 1/4 the price one could use 5200, but that's a permanent adhesive and IMHO not suitable for this application. I think you just don't know when you might need to revisit one of those panels after a close encounter with a fixed object and need to repair or replace.

Ken
 
If I'm correct, even though the majority of the sealant will squeeze out there will still be a layer between the sheets that will form a water tight seal.
 
The key is to clean the mating surfaces. I would use Acetone and scotch bright at least twice. followed by a final wipe with a clean cloth and Acetone. You might consider buying a small bottle of adhesion promoter from the place that sells the sealant. Never buy a sealant with less than 4 hour work life. You cant squeeze all the sealant out from between the joint.
Bill
 
bucks2 said:
Good ideas, but don't Clekos hold the pieces tightly together? I think Whalensdad needs to have the sealant stay between the sheets until cured and then the rivets will hold the pieces in place. If it's squeezed out before cured, then the seal may be compromised.

I see the fuel tank sealant is also an adhesive. If you glue it together with a permanent sealant/adhesive then any future repairs would be extremely complicated or impossible. For 1/4 the price one could use 5200, but that's a permanent adhesive and IMHO not suitable for this application. I think you just don't know when you might need to revisit one of those panels after a close encounter with a fixed object and need to repair or replace.

Ken
You need the two sheets as tightly together as possible. You will never squeeze out all the sealant.
There is no reason not to use a permanent repair in this instance. If needed it can be repaired or replaced as many times as needed.
Bill
 
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